Epoch J2000 Equinox J2000
|Right ascension||19h 02m 43s|
|Declination||+50° 14′ 29″|
|Apparent magnitude (V)||10.960|
|Mass||0.895 ± 0.06 M☉|
|Temperature||5627 ± 44 K|
|Age||11.9 ± 4.5 Gyr|
Kepler-10, formerly known as KOI-72, is a sunlike star in constellation Draco that lies 173 parsecs (564 light years) away from the Earth. Kepler-10 was targeted by NASA's Kepler spacecraft, as it was seen the first star identified by the Kepler mission as a possible host to a small, transiting exoplanet. The star is slightly less massive, slightly larger, and slightly cooler than the Sun; at an estimated 11.9 billion years in age, Kepler-10 is almost 2.6 times the age of the Sun. Kepler-10 is host to a planetary system made up of at least two planets. Kepler-10b, the first undeniably rocky planet, was discovered in its orbit after eight months of observation and announced on January 10, 2011. The planet orbits its star closely, completing an orbit every 0.8 days, and has a density similar to that of iron. The second planet, Kepler-10c, was confirmed on May 23, 2011, based on follow-up observations by the Spitzer Space Telescope. The data shows it has an orbital period of 42.3 days.
Nomenclature and history 
Kepler-10 was named because it was the tenth planetary system observed by the Kepler spacecraft, a NASA satellite designed to search for Earth-like planets that transit, or cross in front of, their host stars with respect to Earth. The transit slightly dims the host star; this periodic dimming effect is then noted by Kepler. After eight months of observation ranging from May 2009 to January 2010, the Kepler team established Kepler-10b as the first rocky exoplanet discovered by the Kepler satellite. Kepler-10 was the first Kepler-targeted star suspected of having a small planet in orbit. Because of that, verifying Kepler's discovery was prioritized by telescopes at the W.M. Keck Observatory in Hawaii. The discovery was successfully verified. Although there had been many potentially rocky exoplanets discovered in the past, Kepler-10b was the first definitively rocky planet to have been discovered.
The discovery of Kepler-10b was announced to the public at a winter meeting of the American Astronomical Society on January 10, 2011 in Seattle. On May 23, 2011, the existence of Kepler-10c was confirmed at the 218th AAS meeting in Boston.
Kepler-10 is a G-type star, like the Sun. With a mass of 0.895 (± 0.06) Msun and a radius of 1.056 (± 0.021) Rsun, the star is approximately 10% smaller than and 5% wider than the Sun. The metallicity of Kepler-10, as measured in [Fe/H] (the amount of iron in the star), is -0.15 (± 0.04); this means that Kepler-10 is about 70% less metal-rich than the Sun. Metallicity tends to play a large role in the formation of planets, determining if they form, and what kind of planet they will form. In addition, Kepler-10 is estimated to be 11.9 billion years old and to have an effective temperature of 5627 (± 44) K; To compare, the Sun is younger and hotter, with an age of 4.6 billion years and an effective temperature of 5778 K.
Kepler-10 is located at a distance of 173 (± 27) parsecs from the Earth, which equates to approximately 564 light years. Also, Kepler-10's apparent magnitude, or brightness as seen from Earth, is 10.96; it therefore cannot be seen with the naked eye.
Planetary system 
Kepler-10b, the first definitively rocky exoplanet, was discovered in the orbit of Kepler-10. The planet has a mass that is 4.56 times that of Earth's and a radius that is 1.416 times that of Earth. The planet's estimated density is 8.8 g/cm³, or 880% that of water. This is similar to that of iron. The planet orbits Kepler-10 at a distance of 0.01684 AU every 0.8375 days; this can be compared to the orbit and orbital period of planet Mercury, which circles the Sun at a distance of 0.3871 AU every 87.97 days. Because the planet orbits so closely to its star, its eccentricity is virtually zero. It, thus, has an extremely circular orbit.
Kepler-10c is an exoplanet that was also discovered by NASA's Kepler Mission in the orbit of Kepler-10. Measurements of the body suggest that it has a mass of at most 0.063 MJ and a radius of 0.199 RJ (2 Earth radii). Kepler-10c would orbit Kepler-10 at a distance of 0.24 AU every 42.29 days.
(in order from star)
|b||4.6±1.2 M⊕||0.01684||0.837495||0||—||1.416 R⊕|
|c||< 20 M⊕||0.2407||42.29485||0||—||2.227 R⊕|
See also 
- "Notes for star Kepler-10". Extrasolar Planets Encyclopaedia. 2011. Retrieved 13 March 2011.
- "Kepler-10 -- Star". SIMBAD. Retrieved 2011-02-01.
- Batalha, N. M.; et al. (2011). "Kepler's First Rocky Planet: Kepler-10b". The Astrophysical Journal 729: 27. arXiv:1102.0605. Bibcode:2011ApJ...729...27B. doi:10.1088/0004-637X/729/1/27.
- Perrotto, Trent J.; Hoover, Rachel (10 January 2011). "NASA'S Kepler Mission Discovers Its First Rocky Planet". Ames Research Center. NASA. Retrieved 13 March 2011.
- "Summary Table of Kepler Discoveries". NASA. 2011. Retrieved 13 March 2011.
- Fressin, F.; et al. (2011). "Kepler-10c, A 2.2-Earth Radius Transiting Planet In A Multiple System". arXiv:1105.4647 [astro-ph.EP].
- "Kepler: About the Mission". Kepler Mission. NASA. 2011. Retrieved 13 March 2011.
- Richard A. Lovett (10 January 2011). "NASA Finds Smallest Earthlike Planet Outside Solar System". National Geographic Society. Retrieved 13 March 2011.
- "Kepler Spacecraft Shows That Smaller Planets Abound". Scientific American. 2011. Retrieved 2011-05-26.
- Henry Bortman (12 October 2004). "Extrasolar Planets: A Matter of Metallicity". Space Daily. Retrieved 13 March 2011.
- Fraser Cain (16 September 2008). "How Old is the Sun?". Universe Today. Retrieved 13 March 2011.
- Ed Grayzeck. "Sun Fact Sheet". Goddard Space Flight Center. NASA. Retrieved 13 March 2011.
- David Williams (17 November 2010). "Mercury Fact Sheet". Goddard Space Flight Center. NASA. Retrieved 27 February 2011.
- "NASA'S Kepler Mission Discovers Its First Rocky Planet". NASA. 2011-01-10. Retrieved 2011-01-10.